Fix a couple performance hints

[thatguy11325]

Cython reports the following performance hints:

  performance hint: pyboy/core/ram.py:29:35: Index should be typed for more efficient access
  performance hint: pyboy/core/ram.py:39:39: Index should be typed for more efficient access
  performance hint: pyboy/core/ram.py:52:31: Index should be typed for more efficient access
  performance hint: pyboy/plugins/debug.py:560:67: Index should be typed for more efficient access
  performance hint: pyboy/plugins/debug.py:575:45: Index should be typed for more efficient access
  performance hint: pyboy/plugins/debug.py:815:27: Index should be typed for more efficient access

Not sure why the ones in debug.py are happening and the first ram hint is in __init__. But I took care of the other two at least.

[Baekalfen]

Awesome! Thank you!